Field of the Invention
The present invention relates to a vibration control device attached aslant between two structural members such as a pillar and a beam of a structure to suppress vibrations of the structure when an earthquake hits.
Description of the Related Art
Hitherto, there is known a structure vibration control device using a hydraulic damper as disclosed in Japanese Patent Application Nos. H06-346625, H10-227145, and 2000-54677, for example. The hydraulic damper described above includes a cylinder configured such that a hydraulic chamber formed therein is partitioned by a piston into oil chambers and a piston rod is inserted through wall surfaces provided at both ends of the hydraulic chamber. The hydraulic damper constitutes a brace damper by diagonally connecting a piston rod side to one structural member and a cylinder side to another structural member, and damps vibrations of the structure caused by an earthquake by circulating viscous fluid (oil) of both oil chambers through a restricted oil passage.
Because the piston rod penetrates through the hydraulic chamber, no volumetric change occurs in the hydraulic chamber even if the piston rod is moved.
The hydraulic damper described above installed on a wall surface, within an attic or the like of a building is liable to be affected by atmospheric temperature and sun radiation and its ambient temperature ranges from below zero to 50° C. The hydraulic damper is also exposed to annual variations of spring, summer, autumn and winter and daily variations of day time and night time. The variation of ambient temperature affects the oil (viscous fluid) filled in the hydraulic chamber of the hydraulic damper, and the oil repeats expansion and contraction.
The hydraulic damper described above is constructed such that no volume change occurs in the hydraulic chamber by the move of the piston rod as described above and such that the volume of the hydraulic chamber formed of the cylinder and the both end wall surfaces is invariant. Due to that, if the oil expands/contracts due to the temperature variation, pressure of the oil in the hydraulic chamber largely varies and acts on sealing of the wall surfaces through which the piston rod is slidably and fittingly inserted. Then, there is a possibility of leaking the oil out of the hydraulic chamber and of permitting outside air to enter the hydraulic chamber, thus quickly deteriorating functions of the hydraulic damper.
Accordingly, the present invention aims at providing a structure vibration control device configured such that a volume of a hydraulic chamber of a hydraulic damper can be varied and damping force characteristics thereof varies corresponding to magnitude of an earthquake, thus making it possible to maintain its function over a period of time.